1. Field of the Invention
This invention relates to implantable techniques for infusing a therapeutic agent into an organism and more particularly relates to such techniques for delivering such a therapeutic agent with a patient's own endogenous fluid.
2. Description of the Related Art
When chronic administration of a pharmaceutically active agent is required, internal delivery by an implantable infusion pump ("IIP"), in combination with a catheter, may be the desired delivery means. For example, IIP-catheter delivery may be preferred when the site specific delivery of the agent is critical, or the agent must be administered to spaced sites in tightly controlled, yet minute dosages.
Experience has shown for minute dosages, the therapeutic agent may require buffering or dilution before being administered to the body, particularly if the parenchyma of the brain is the target organ. Certain proteins may need to be formulated at a pH different from the neutral pH optimal for safe delivery to the brain parenchyma. For example, a drug agent may need to be stored at an acidic or basic pH to achieve stability at body temperature, but it may need to be delivered into the brain parenchyma at or near neutral pH.
Experience has shown that the catheters used to administer the agent may require continuous or near continuous flow, even if therapeutic agent infusion is intermittent, in order to prevent clogging. However, it is difficult to provide continuous flow of relatively large volumes of fluid from an implanted pump, because the reservoir in such pumps necessarily has limited volume. The present invention is directed to solving the foregoing problems.